Conventionally, a general substation for electric railcars converts AC power, supplied from, for example, an electric power company, to DC power and supplies the DC power to a feeder. Electric vehicles receive the DC power from the feeder through an overhead contact line to run. In the case of subways and the like, the electric power is supplied through a third rail, instead of the overhead contact line.
When the electric vehicle accelerates, the electric power supplied through the overhead contact line is supplied to a running motor through an electric power controller mounted on the vehicle. Thus, electric energy is converted into running energy, and the electric vehicle runs. When the electric vehicle accelerates, the electric vehicle requires a large amount of electric power. Therefore, the voltage of the overhead contact line or the like drops. Although it depends on the degree of the voltage drop, the voltage drop of the overhead contact line may adversely affect the running of the other electric vehicle running in the same section.
When an electric vehicle having a regeneration capability decelerates, running energy of the electric vehicle is converted into electric energy by using the running motor as a power generator. The obtained electric power is called regenerative electric power.
To return the regenerative electric power to the overhead contact line, an electric power controller mounted on the electric vehicle performs a control operation of increasing the voltage of the overhead contact line. Therefore, the voltage of the overhead contact line generally increases.
Of course, if another electric vehicle running at the same time as the above electric vehicle is accelerating, the regenerative electric power is consumed by the other electric vehicle. However, if there is no electric vehicle consuming the regenerative electric power, the voltage of the overhead contact line increases, and the electric power controller performs a control operation of suppressing the generation of the regenerative electric power in the electric vehicle when the voltage is equal to or higher than a certain voltage. This operation is generally called regenerative reduction. Further, if the voltage of the overhead contact line increases more, the electric power controller of the electric vehicle performs a control operation of terminating the regeneration. This operation is generally called regenerative invalidation.
If the regenerative reduction or the regenerative invalidation occurs, a mechanical brake is activated to obtain necessary deceleration, and the running energy is converted into heat energy to be dissipated.
To prevent the regenerative invalidation, a method may be used, in which to consume the regenerative electric power in the substation, a chopper is used, and the regenerative electric power is converted into the heat energy by an electric resistor. However, even in this case, the regenerative electric power is wastefully dissipated.
Moreover, to prevent the regenerative electric power from being wasted, there is a method in which: for example, an inverter configured to convert the regenerative electric power into the AC power is provided in the substation; surplus regenerative electric power is converted into the AC power having commercial power frequency; and the AC power is transmitted inversely or is utilized in stations and the like. In this case, although the regenerative electric power can be effectively utilized, this method requires an expensive inverter.
Also proposed is that: a large-scale battery system is provided in a substation; a surplus regenerative electric power is accumulated by charging the battery system with the surplus regenerative electric power; the battery system discharges the surplus regenerative electric power when the voltage of the overhead contact line drops; and thus the voltage drop of the overhead contact line is suppressed (see PTL 1, for example). Such a battery system has been attracting attention from the viewpoints of the effective utilization of the regenerative electric power and the retention of the running performance by the retention of an appropriate voltage of the overhead contact line.
Proposed is an electric power supply system which realizes the effective utilization of the regenerative electric power by using a battery system provided in a substation without using a charge and discharge controller and complements an electric power transfer capability of the substation (see PTL 2, for example).